US 2010/0005790 A1 describes a tubular flow element which deflects the exhaust gas stream at an angle of between 40° and 50° away from the main flow direction, and in which the exhaust gas stream is mixed with an additive. The wall of the flow element is perforated continuously in the flow direction, so that the exhaust gas stream penetrates into the flow element over the entire surface of the wall.
JP 2009 030560 A discloses a mixing device in which a plurality of converters are arranged in the flow-guiding element, which converters help to mix the additive.
US 2011/0094206 A1 describes an injection device in which the additive is injected into the parallel exhaust gas flow.
DE 11 2010 002 589 T5 already describes a mixing chamber arranged between two monoliths (substrates). This mixing chamber is arranged between the monoliths in order to treat the exhaust gases circulating in the exhaust tract. The mixing chamber has a channel, which is formed by a shell and which encloses the central axis, for circulating the exhaust gas stream, said channel being at least 20% longer than the mixing chamber along the central axis.